Previously, for example, Patent Document 1 discloses a valve operating mechanism of an internal combustion engine in which a cam carrier provided with two kinds of cams is provided for each cylinder, and the cam carrier is moved in the axial direction with respect to a cam main-shaft which is rotated so that valve drive cams for each cylinder are switched. To be more specific, in this conventional valve operating mechanism, guide grooves which are formed into a helical shape are provided respectively in both ends of the outer peripheral surface of each cam carrier. Moreover, an electric actuator, which drives a drive pin to be inserted into or removed from the guide groove, is provided for each guide groove.
According to the above-described conventional valve operating mechanism, the cam carrier can be moved with respect to the axial direction by inserting the drive pin to the guide groove, and thus the lift amounts of valves can be changed by switching the valve drive cams of each cylinder. Moreover, in the above-described conventional valve operating mechanism, the above-described electric actuator is disposed outside a cylinder head.
Including the above-referenced document, the applicant is aware of the following documents as a related art of the present invention.    [Patent Document 1] National Publication of International Patent Application No. 2006-520869    [Patent Document 2] Japanese Patent No. 2663556    [Patent Document 3] Japanese Laid-open Patent Application Publication No. Hei 11-235000    [Patent Document 4] Japanese Laid-open Patent Application Publication No. 2004-124794    [Patent Document 5] Japanese Laid-open Patent Application Publication No. 2008-196462    [Patent Document 6] Japanese Utility Model Publication No. Hei 07-23558